The present invention relates generally to pneumatic tires, and more specifically to pneumatic tires designed to remain affixed to and in operative association with the vehicle rim even upon deflation of the tire. Some varieties of these tires include devices designed to support the vehicle when the tire loses inflation pressure. Such tires are commonly known as xe2x80x9crun-flatxe2x80x9d tires.
The performance of a tire depends on the retention of pressurized air within the tire. Upon a condition where the pressurized air in the tire escapes, such as when the tire is punctured by a nail or other road hazard, performance of the tire can diminish rapidly. In most cases, the vehicle can only be driven a very short distance before it becomes inoperable.
One problem in providing continued performance upon deflation of a tire is retention of the tire on the rim. Since the tire is normally retained on the rim by the pressurized air within the tire, pushing the beads and sidewalls of the tire outwardly against a rim flange, the escape of the pressurized air through a puncture or other means, eliminates the inner pressure. Absent this pressure, the tire may slip off the rim, and control of the vehicle becomes difficult.
Previous efforts to prevent separation of the tire from the rim have used a special rim/tire combination. One of the reasons this solution has not been widely implemented is the high cost of the special rims which are required. Also, rim/tire combinations of this type sometimes require special mounting procedures and/or equipment. For these reasons, they have never been commercially acceptable.
There was perceived a need for a new tire which could stay connected to a conventional rim, even in a deflated condition, without the requirement of a special rim. In other words, a tire which could be mounted to any conventional rim, but which would be retained upon the rim upon tire deflation and would continue to provide acceptable driving performance for an acceptable distance.
Efforts by others to address this need include European Patent application 0 475 258 A1; U.S. Pat. No. 5,131,445; U.S. Pat. No. 3,954,131; U.S. Pat. No. 4,193,437; U.S. Pat. No. 4,261,405, and European Patent application 0 371 755 A2.
Charvat, in U.S. Pat. No. 4,794,967, issued Jan. 3, 1989, discloses a tire having a bead ring comprising a stack of ribbons having a curved shape. The concavity of the ribbons is described as facing the axis of rotation of the tire. The ribbons also have an angle xcex1xe2x89xa7xcex2+5 (where xcex2 is positive) or an angle of xcex1xe2x89xa75 if xcex2 is negative. xcex2 is defined as the angle of the bead seat of the rim, and xcex1 and xcex2 are expressed in degrees.
In addition, several other attempts have sought to develop a bead configuration having certain advantageous properties and configurations. For example, in U.S. Pat. No. 4,203,481 a run-flat tire is disclosed which is to be used in association with a special rim. In U.S. Pat. No. 1,914,040, a tire bead is disclosed having a rectangular configuration. Further, in U.S. Pat. No. 1,665,070, a tire bead is disclosed having a triangular configuration.
In commonly owned U.S. Pat. No. 5,679,188 and U.S. Pat. No. 5,368,082, which are incorporated herein by reference, an innovative run-flat device utilized an inventive bead core which satisfies the needs of run-flat tires.
The inventive tire as described below has a bead core which retains its shape without requiring an additional step of pre-curing the rubber coated core. This is made possible by the shape and angular orientation of the cross-section sides of the bead core, and their angular relationship with the surrounding elastomeric heel and toe surfaces as described below.
Heike van de Kerkhof of DuPont(copyright), at Tire Technology International 1997, pp. 52-55, describes the use of Kevlar(copyright) brand fibers in high performance tires, and suggests the use for such fibers can be extended to standard passenger tires. At page 54, the suggestion is made that some fabrics can be replaced by fiber loaded composites.
EPA 0329589 of The Goodyear Tire and Rubber Company describes aramid-reinforced elastomers. The aramid reinforcement is described as short, discontinuous, fibrillated fibers. The reinforced elastomers are used as components of pneumatic tires, where the components can be reinforcing belts, sidewall members in the region of the beads, a belt overlay, edge strips or tread.
The present invention relates to a pneumatic tire (10) which can be used on a conventional rim (22) and which will be retained on the rim (22) even upon deflation of the tire (10). The inventive tire (10) is a vulcanized radial ply pneumatic tire having a pair of axially spaced annular beads. Each of the beads (25) has a substantially inextensible bead core (20) which comprises a coil of round wire filaments (26) or a single continuous filament (26), which is built into the toroidally-shaped tire (10) prior to its vulcanization. At least one radial ply (17) extends between the beads (25) and is preferably turned radially outwardly around the bead cores (20). The bead core (20) is further characterized by a polygonal cross section having a radially-inward base side (44), the base side (44) having a first edge (54), a second edge (56) and a length extending between the first and second edges, a radially outward side (46), a first side (48) and a second side (50). The first and second sides (48) and (50) extend from the base side (44) toward the radially outward side (46). The first side (48) meets the base side (44) through first edge (54) and the second side (50) meets the base side (44) through second edge (56).
The inventive tire (10) can be used in connection with a rim (22) having a flange (76) and a hump (80). A bead heel surface (60) on the tire (10) can be configured to have a length between 85% and 100% of the distance W between the hump (80) and an axially inward surface (74) of the flange (76), contributing to the tire (10) remaining on the rim (22) during a deflated condition. Wire filaments (26) or filament windings in a first wire layer of the bead core can be configured so that a relatively wide, stiff first layer can be constructed, further contributing to the retention of the tire (10) on the rim (22) upon a deflated tire condition.
The bead core base side (44) is inclined at an angle xcex1 of 15xc2x0 to 30xc2x0, preferably 15xc2x0 to 25xc2x0 relative to the axis of rotation of the bead core, which should be coincident with the tire axis of rotation when mounted on the tire""s design rim, the length of the base side (44) being at least 50% of the width of the bead heel surface (60), preferably in the range of 50% to 85% of the width of the bead heel surface (60).
The bead heel surface (60) has a central portion (61), a heel portion (65) and a toe portion (63). The central portion (61) is radially inward of the bead base side (44) and has an angle xcex2 of 10xc2x0 or greater relative to the bead core axis of rotation and at least 4xc2x0 less than the angle xcex1 of the base side (44). The central portion (61) has a width of at least 50% of the length of the base side (44), preferably 50% to 100% of the length of the base side (44).
In the illustrated embodiment, the bead heel (65) has a radius of about 0.25 inch (0.64 cm).
Also included in the invention is a rubber composition comprising, in parts by weight per 100 parts rubber (phr): 90-40 phr cis-1,4-polybutadiene rubber, 10-60 phr polyisoprene, 40-100 phr carbon black, and 0-30 phr silica. The rubber composition of the invention has a 300% modulus of 8 to 13 MPa, a tensile strength at break of 13 to 19 MPa, an elongation at break of 300 to 600%, RT Rebound of 48 to 58, a tan delta at 10% strain and 100xc2x0 C. of 0.13 to 0.19, Gxe2x80x2 at 1% strain of 1900 to 2700 KPa, and a Gxe2x80x2 at 50% stain of 700 to 1100 KPa. In one embodiment of the compound of the invention, the compound may also include 0.5 to 6 phr kevlar pulp.
Also claimed is a tire rubber component made using a compound of the invention.